Automatic switchover system for radio relay



Jan. 11, 1955 H. MAGNUSKI ETAL AUTOMATIC SWITCHOVER SYSTEM FOR RADIORELAY Filed Oct. 3, 1950 4 Sheets-Sheet 1 i v a m R U n m M m W mi w W HW 0E W a? E 55 nr :6 5 W CmEQ cw J fioEmfiwW 5: 5 222$ s: c a n w E2m w63:22. 3). E2 525 mm 28222 5 5 S E W M Q E5 E5 Es E5 395m 3 m Ea: 395522 3 United States Patent AUTOMATIC SWIT'CHOVER SYSTEM FOR RADID RELAYHenry Magnuski and Willis J. Steen, Chicago, Ill., as-

signors to Motorola, Inc., Chicago, 111., a corporation of IllinoisApplication October 3, 1950, Serial No. 188,186

16 Claims. (Cl. 250-45) This invention relates generally to a system forsensing failure of radio equipment and more particularly to a failuresensing system for use with microwave relay equipment to automaticallyswitch from a main unit to a standby unit in the event of failure of themain unit.

Radio equipment is being used to provide commu nication in manyapplications in which dependable continuous operation is highlyessential. One important application of this type is microwave relaysystems which may be used to provide a plurality of channels over longdistances. In such systems it is desirable to locate the relay points atas high an altitude as possible and in many cases the relay stations areplaced on mountain tops or other relatively inaccessible places. Thesesystems do not require the continuous attendance of an operator as theyare completely automatic, and to provide a dependable continuousoperation it has been proposed to provide a standby or spare unitwhichcan be connected when a failure occurs in any part of the mainunit.

Because of the complexity of the microwave relay equipment, it must beexpected that failures will occasionally occur. Each microwave repeaterstation may have approximately fifty vacuum tubes of various differenttypes which have relatively limited life. In a microwave relay systemcovering 1,000 miles, it would be expected that there would beapproximately fifty repeater stations making a total of 2,500 vacuumtubes in all. The average life of such tubes will probably be not morethan 20,000 hours and after the tubes became old it could be expectedthat in such a system a tube would fail every eight hours. It is obviousthat some time would be required to find the tube failure and repair itand that either during this time or immediately thereafter anotherfailure might occur, so that the relay system might be out of operationa large percent of the time. From the above it is apparent that theprovision of a standby or spare unit which can be connected in thissystem is essential for continuous dependable operation.

Since an operator is not always present at the relay stations, automaticswitchover equipment must be provided for switching in the standbyequipment. It is also desirable that the switchover system give someindication to another station, such as a terminal station where anoperator may be present, so that a maintenance man can be sent to theequipment which has failed for repairing the same. After such repair therelay system can then be changed back to the main unit and in the eventof another failure the standby unit will be available to beautomatically switched in. The sensing equipment must be effective todetect the failure of any component of the main unit at a particularstation but must not operate in the event of failure of equipment atanother, station. For example, at a relay station a signal might not bereceived due to failure of the transmitter at another station with whichthe relay station is communicating, and in such case the sensingequipment must not respond. .However, the sensing equipment must behighly responsive to failure of equipment at each relay station.

It is therefore an object of the present invention to provide animproved failure sensing system for use with communication equipment.

It is another object of this invention to provide a systern for sensingfailure of the components of the receiving portion of the microwaveequipment at a relay station which is effective independently ofoperation of the transmitting portion of the station with which it is incommunication.

A further object of this invention is to provide a simple and dependablesystem for automatically switching from the main unit at a microwaveradio relay station to a standby unit in response to failure of anycomponent of the main unit.

A still further object of this invention is to provide a system forsensing failure of communication equipment for switching in standbyequipment which automatically checks to determine that the faultcontinues for a predetermined time before switching in the standbyequipment.

Still another object of this invention is to provide an automaticswitchover system for connecting standby equipment in the event offailure of main equipment, which is operative to connect power to thestandby equipment for a predetermined time interval to condition thestandby equipment for operation and thereafter switch the operativeconnections from the main to the standby unit.

A feature of this invention is the provision of a system forautomatically sensing defective operation of com-. ponents of radioequipment in which certain components are checked by the outputtherefrom and certain other components are checked by their efiiciencyin transmitting a test signal.

Another feature of this invention is the provision of a system forsensing failure of components of a microwave unit in a relay system byapplying a low frequency test signal to the local oscillator of thereceiving portion of the unit and deriving the test signal from thevideo amplifier of the transmitting portion, with the operation of thecomponents being indicated by the efficiency with which the test signalis transmitted therethrough.

A feature of this invention is the provision of equipment for sensingfailure of a microwave receiving portion which transmits noise in theabsence of a signal, in which a low frequency signal is applied to thelocal oscillator of the receiving portion for modulating the same to asmall extent and sensing means is connected to the out put of thereceiving portion which indicates the presence of the low frequency testsignal and/or noise, whereby the presence of the low frequency signalindicates proper operation of the receiving unit when a signal is beingreceived and the presence of noise indicates proper operation in theabsence of a received signal.

A still further feature of this invention is the provision of failuresensing equipment for automatically checking all components of amicrowave relay system, which checks back to determine if a defect whichappears continues over a predetermined time. The equipment auto--matically switches a standby unit into the system in place of the mainunit when the defect continues for the predetermined time.

Still another feature of this invention is the provision of equ'pmentfor automatically switching a standby unit into a system in the event ofdefective operation of a component of the main unit, with the equipmentchecking to determine that the fault continues for a predetermined timebefore starting the switchover operations, and then energizing thestandby unit for another predetermined period so that it is completelyoperative before the circuits are connected from the main unit to thestandby unit. In this way, the main unit remains in the system and mayprovide communication, even though somewhat defective, until the standbyunit is in full operative condition.

Further objects and features of the invention will be apparent from aconsideration of the following description when taken in connection withthe accompanying drawings in which:

Fig. l is a block diagram illustrating the application of the failuresensing and automatic switchover system to a microwave relayinstallation;

Pig. 2 is a block diagram illustrating the equipment required forproviding automatic switchover at a terminal station;

Fig. 3 is a block diagram illustrating the equipment for providingautomatic switching at a relay station;

Figs. 4 and 5 are circuit diagrams of the sensing apparatus forindicating the presence noise; and

Fiig. 6 is a circuit diagram of the switchover panel.

In practicing the invention the failure sensing and switchover system isapplied to a microwave relay 1nstallation including two terminalstations and one or more intermediate relay stations. At each stationthere are provided main and standby units for transmitting and receivingmicrowave signals which may be of substantially identical construction.In general, these units may be entirely separate and independent,including the power supplies therefor, and are selectively connected toa common antenna through a wave guide switch. The sensing systemincludes three circuits which together check all the components of themain unit. The transmitting portion of the main unit is checked by meansat the antenna which responds to the output of the transmitting portion.The local oscillator and mixer of the receiving portion are checked bymeans at the output of the mixer which is responsive to the amplitude ofthe output. The intermediate frequency amplifier, detector, and thevideo amplifier of the main unit are checked by the use of a testsignal. This test signal is used to modulate the local oscillator to asmall extent and is thereby applied through the mixer when a signal isbeing received to the intermediate frequency amplifier and detector. Inthe absence of a received signal, noise is present which appears at theoutput of the detector. Therefore, either the test signal or noise ispresent when the system is operating properly. A selective amplifierwhich responds to the test signal and to noise is connected to theoutput of the detector and operates through a rectifier and relay toindicate defective operation of the intermediate frequency amplifier.The test signal may also be applied through the video amplifier to checkthis component, being separately applied in the terminal stations, andbeing applied from the detector directly to the video amplifier throughthe existing connection in the relay stations.

The various indications of defective operation are applied to aswitchover panel and any one of the indications starts the operation ofa timer mechanism. The timer mechanism continues to check to determineif the defecof the test signal and tive operation continues for apredetermined time, and if the defective operation does continue for thepredetermined time, starts the switching operation for connecting in thestandby unit. The switchover panel causes energization of the standbyunit and after sufiicient time for the standby unit to warm up switchesthe circuits and antenna from the main unit to the standby unit. Themain unit remains in circuit until the standby unit is in completeoperating condition so that the main unit, although defective, mayprovide partially effective operation.

In Fig. 1 there is illustrated a microwave relay installation includingterminal stations A and B and relay station C. The terminal station Aincludes a main microwave unit 10 and a standby microwave unit 11. Theseunits are connected to a waveguide switch 12 which selectively couplesone of the units to the antenna 13. For controlling the Waveguide switchthere is provided an automatic switchover system 14 which includes equipment for sensing defective operation of the main transmitter-receiverunit 10 and operates to disconnect the main unit 10 from the antenna 13and connect the standby unit 11 thereto. A power indicator 16 isprovided along the waveguide between switch 12 and the antenna 13.Signalling equipment which may be of the type providing multiplexoperation is connected to the main and standby units for applyingsignals thereto and deriving signals therefrom. This signallingequipment may be connected to the units through the automatic switchoversystem 14 so that the signalling equipment is connected only to the unitwhich is operative at any time if this is desired.

The terminal station B includes main microwave unit 20 and standbymicrowave unit 21 which are coupled through the waveguide switch 22 tothe antenna 23. A power indicator 26 is provided as at station A. Anautomatic switchover system 24 and signalling equipment 25 are alsoprovided at the terminal station B. All of the components at theterminal station B may be identical with those at terminal station A andoperate in exactly the same manner.

At the relay station C, two sets of equipment are provided forcommunicating with stations A B respectively, with each set of equipmentbeing s1milar to that at each terminal station. For communicating withterminal station A, a main microwave unit 30 is provided which isconnected through waveguide switch 32 to antenna 33. The waveguideswitch selectively connects the main unit 30 or the standby unit 31 tothe antenna 33. For simplicity the portion of the relay stationcommunicating with the terminal station A will be called the west unit.Similarly the portion communicating with terminal station B will becalled the east unit and includes main microwave unit 34, standbymicrowave unit 35, waveguide switch 36 and antenna 37. For controllingthe connection of the standby units 31 and 35, an automatic switchoversystem 38 is provided which is similar in operation to the automaticswitchover systems 14 and 24 at the terminal stations. This systemoperates to detect failure of the main units 30 and 34 and in such eventto connect the standby units 31 and 35 to the antennas. The relaystation may be what is called a straight through repeater station inwhich all of the signals are retransmitted and the individual signalsare not derived at the relay point. Alternatively, it may be desired toreceive or transmit signals at the relay station C over one or more ofthe channels of the system, and in this event signalling equipment 39will be required.

In Fig. 2 there is shown more in detail the application of the sensingand switchover system to a terminal station such as terminal station Aof Fig. 1. The system includes main microwave unit 10, standby unit 11,waveguide switch 12 connected to antenna 13, control cabinet 18 andsignalling equipment 15. Components of the main unit 10 are shown inblock diagram. The transmitting portion of the unit 10 includes atransmitter oscillator 40 to which signals are applied by videoamplifier 41. The transmitter oscillator may be any suitable microwavetube such as a klystron or a magnetron, and applies a modulatedmicrowave signal to the antenna for transmission thereby. The signalreceived by the antenna is applied to the receiving portion of the unit10 which includes mixer 42, local oscillator 43 and intermediatefrequency amplifier and detector unit 44. The construction of. thesecomponents of a microwave unit may be standard.

For sensing failure of the components of the main microwave unit, anautomatic switchover system is provided. The switchover equipment in thecontrol cabinet 18 together with certain components shown connecteddirectly to components of the transmitter-receiver unit make up theautomatic switchover system 14 of Fig. 1. For checking the operation ofthe transmitting portion, a power indicator device 16 for detecting thepower output of the transmitter, such as a crystal detector, may beprovided. In Fig. 2 this power indicator device is illustrated as beingincluded above the waveguide switch 12 in the line feeding antenna 13.This device is connected through conductor to the power meter 51 and tothe transmitter sensing unit 52 in the control cabinet 18. Similarly, adetecting device responsive to the output of the receiver mixer 42 maybe incorporated in the mixer and connected through conductor 53 to meter54 and to the sensing unit 55 for the local oscillator and mixer. Thesensing units 52' and 55 respond to the amplitude of the signals appliedthereto, and as will be explained are connected to the switchover panel58 to cause switchover operation to take place when the signals fallbelow particular values.

For checking the operation of the video amplifier 41 and theintermediate frequency amplifier and detector 44, a test signal isapplied through these components. This may be a signal of any convenientfrequency which does not interfere with thecommunications passingthrough the system. A cycle signal which is readily obtainable may beprovided by a source 56 to the video amplifier and be passedtherethrough simultaneously with the normal communication signals.Connected to the output of the video amplifier 41 is an amplifier-relayunit 57 which is selective to the 60 cycle signal and causes operationof the relay when the 60 cycle signal is not received thereby at acertain level. The amplifier-relay unit 57 is connected to theswitchover panel 58 in the control cabinet. A passive filter 59 isprovided for preventing application of the 60 cycle test signal to thetransmitter 40.

The intermediate frequency amplifier 44 may also be checked by applyingthe test signal therethrough. The

60 cycle signal from the source 56 may be applied to the localoscillator 43 to modulate the oscillator to a slight extent. When asignal is being received from the antenna 13 and applied to mixer 42,the 60 cycle modulation which is applied to the local oscillator appearsin the output of the mixer and is applied through the intermediatefrequency amplifier 44 to the detector portion thereof wherein it isdetected. Connected to the output of the intermediate frequencyamplifier and detector 44 is a selective amplifier-relay unit 60 whichis responsive to the 60 cycle test signal andto noise signals. When asignal is not being received and applied tothe mixer 42, the output ofthe local oscillator 43 will not appear at the output of the mixer.However, under these conditions the receiver will provide noise whichwill be amplified in the intermediate frequency amplifier and will beapplied to the amplifier relay unit 60. The unit 60 is arranged so thatwhen either the noise signal or the 60 cycle signal is applied theretoat or above a certain level no operation will take place but when thesignal applied to the unit, which may be either the 60 cycle test signalor noise, falls below the certain level the relay of the unit willoperate and will apply a signal to the switchover panel 53 in thecontrol cabinet 18.

As will be more fully explained, the switchover panel is effective, whenany one of the sensing units operates, to energize the standby unit 11,operate the waveguide switch 12 to connect the standby unit .11 to theantenna 13, and then deenergizc the main unit 10. The panel may alsoinclude a switch 61 for connecting the signalling equipment 15 to thestandby unit 11 instead of to the main unit 10. However, in most casesthe signalling equipment may feed both the main and standby unitssimultaneously.

In Fig. 3 there is illustrated more in detail the application of theautomatic switchover system to a relay station such as the relay stationC of Fig. 1. The main microwave units 30 (west) and 34 (cast) are shownin block diagram. The components of these units are the same as shown inFig. 2 and will be identified by the same reference numbers. Theoperation of the transmitters 40 may be checked by means of powerindicators with the power indicator 63 of the west unit being connectedto meter contact 64 and the west transmitter sensing unit 65. Similarlythe power indicator 66 of the east unit is connected to the east metercontact 67 and to the east transmitter sensing unit 68. The mixers 42may also include detecting means with the west mixer being connectedthrough line 69 to the meter 70 and sensing unit 71 and the east mixer72 to the meter 73 and sensing unit 74.

At the relay stations the equipment for detecting failure of the videoamplifier and the intermediate frequency amplifier and detector may becombined to thereby simplify the equipment required. A test signal,which may be of 60 cycles is provided from source 75 to the main unit 30and is coupled to the local oscillator 43 thereof for modulating thisoscillator. The modulated signal is applied through mixer 42 tointermediate frequency amplifier and detector 44 in which the level ofthe test signal is increased and the 60 cycle signal is then derivedfrom the modulating wave. The 60 cycle signal is then amplified alongwith the communications signal through the video amplifier 41 of theunit 34 and applied from the output thereof to the amplifier-relay unit76. The amplifier of the unit 76 responds to the 60 cycle signal andalso to noise signals so that a substantially fixed output is providedthereby whether or not a signal is being received. The relay of the unitis arranged to operate when the output of the amplifier falls below apredetermined value which indicates defective operation of theintermediate frequency amplifier, the detector, or the video amplifier.The amplifier-relay unit 76 is connected to the switchover panel 77 inthe control cabinet 17. In order to prevent transmission of the 60 cyclesignal through thetransmitter 40 of the unit 34 and to the antenna 37, afilter 78 is provided between the video amplifier 41 and 'fihetransmitter 40 which rejects the 60 cycle test signa An exactlyidentical system is provided for checking the operation of theintermediate frequency amplifier and detector 44 of the unit 34 and thevideo amplifier 41 of the unit 30. This includes as test signal source80 con nected to the local oscillator 43 of the unit 34, the amplifier-relay unit 81 connectedto the video amplifier 41 being connectedthrough line (ill of the unit 30, and the filter 82 interposed betweenthe video amplifier 41 and the transmitter 40 of the unit 30 to rejectthe 60 cycle test signal. The relay of the amplifier relay unit 81 isconnected to the switchover panel 83 in the control cabinet 17. The testsignal sources 75' and 80 of the two units 30 and 34 may be combined ifdesired.

As shown in Fig. 3, the switchover panel 77 is connected to the sensingunits of the west microwave unit 30 and responds to failure of anycomponent thereof to energize the standby unit 31 and connect the sameto the antenna 33 through the waveguide switch 32. Similarly, theswitchover panel 83 responds to the various sensing units of the eastmicrowave unit 34 and in response to failure thereof energizes standbyunit 35 which connects the same to antennas 37 through waveguide switch36. It is to be noted that a single switchover panel might be used forboth east and west units with the various sensing units being coupledthereto, and in the event of failure of any component of either unit,both standby units 31 and 35 would be simultaneously connected inoperation.

I11 Fig. 4 there is illustrated the detail circuit of theamplifier-relay unit for detecting the presence of the 60 cycle testsignal and noise. The circuit of Fig. 4 is particularly adaptable to beused as the unit indicated at 60 in Fig. 2 which is connected directlyto the output of the intermediate frequency amplifier and detector unit'44. The circuit includes an input terminal adapted to be connected tothe output of the detector and includes two wide band amplifier stages91 and 92 for amplifying the 60 cycle test signal, and noise signals inthe range from a few cycles per second to several thousand cycles persecond. The output of the amplifier stages are applied to rectifier 93which produces a negative direct current output. The negative directcurrent voltage is applied to tube 94 having a relay 95 connected in theoutput circuit thereof. This relay is normally held open by the 60 cyclesignal and the noise signal and when components operate defectively sothat the 60 cycle test signal and the noise signal both fall below apredetermined level, the relay 95 will drop out so that the contact 96will close and the line 97 will be connected to a source of potential.The line 97 is connected to the circuit of the switchover panel as willbe more fully explained.

Fig. 5 illustrates a similar amplifier-relay circuit to be used at theoutput of the video amplifier. This circuit can be used for the unitdesignated 57 in Fig. 2 and the units designated 76 and 81 in Fig. 3.The principal difference of the circuit of Fig. 5 and that of Fig. 4 isthat less amplification is provided in Fig. 5 since the signals appliedto this unit have been passed through a video amplifier 41 and are atrelatively high level. The output from the video amplifier is applied tothe input terminal 100 and amplified in the stage 101. Rectifier 102provides a negative direct current voltage from the signal and thisnegative direct current voltage is amplified in the tube 103. Relay 104is connected in the plate circuit of the tube 103 and holds the contact105 thereof open when 60 cycle or noise signals of a predetermined levelare applied to the unit. When the level of the signals fall below apredetermined value, the relay drops out and the line 106 connected tothe switchover panel is connected by the contact 105 of the relay 104 toa source of potential.

Reference is now made to Fig. 6 in which the circuit of the switchoverpanel and certain of the sensing units is illustrated. The circuit willbe described in connection with a terminal station as illustrated inFig. 2 although it is also applicable for use at a relay station. Thecircuit includes an input terminal 110 to which the voltage from thepower indicator 16 is applied. This voltage is a measure of the outputof the transmitter '40 at the desired transmitting frequency. Inputterminal 111 is provided to which the voltage from the detector of themixer 42 is applied with this voltage representing the output of themixer crystal. The signal applied to the input terminals 110 and 111 areapplied to sensitive relays 112 and 113 respectively which may be of thetype commonly known as sensitrols. These relays include main energizingwindings 114, permanent magnets 115, movable armatures 116 and resetsolenoids 117. The relays .112 and 113 can be adjusted so that when thevoltage applied thereto drops below a critical point, the armatures 116will be drawn to the magnets 11S closing a circuit therethrough. Thearmatures are connected through conductors 118 and 119 to one terminalof a source of potential which is designated as the A. C. common bus.The relays 112 and 113 are effective to complete the connection from theA. C. common bus to the conductor 120.

The switchover panel also includes input terminals 121 and 122 which areconnected to the conductor 120. The terminals 121 and 122 may beconnected to the amplifier and relay units 57 and 60 of Fig. 2 which areshown in detail in Figs. and 4 respectively. The conductors 97 and 106of the amplifier-relay units are connected to the terminals 121 and 122so that when the relays of these units drop out due to defectiveoperation of components of the main microwave unit, the terminals 121and/or 122 will be connected to the A. C. common bus. It is seen fromthe above that failure of any component of the main "unit of theterminal station will operate through one of the sensing units to causethe lead 120 to be connected to the A. C; common bus.

The lead 120 is connected to timer 125 to cause operation thereof. Theother terminal of the timer is connected through conductor 126 andcontact 127 of relay 128 to the other side of the A. C. line. The relay128 is the main energizing relay for the main microwave unit and isnormally closed. This relay energizes the filament supply of the mainunit 10 and operates through delay unit 129 to energize the platesupply. The plate supply is connected after the filament supply toprotect components of the main unit in a manner that is well known. Thetimer 125 is adapted to operate for a predetermined time and then closethe contacts 130 thereof. A projection 131 schematically represents theclosing arm for the contacts.

Connected in parallel with the timer 125 is a motor 132 which drivestoothed wheels 133 and 134. Bearing against the toothed wheel 133 is aswitch contact 135 which is allowed to close when it engages therecesses 136 in the wheel. The contact 136 causes energization of thereset solenoids 117 of the relays 112 and 113 so that these relays areintermittently interrupted. The interrupting provisions are necessary asthe relays stay locked after they are once actuated and it is necessaryto reset them to determine if the voltage applied to the main windingsthereof which indicates a failure continues. Contact 138 bears againsttoothed Wheel 134 and is allowed to close when it engages the recesses139 therein. The recesses 139 are arranged so that the contact 138closes before the contact 135 and stays closed until after the contact135 is opened. The contacts 138 connect the conductor 120 to theconductor 118 so that the energizing potential is applied to the timer125 while the relays 112 and 113 are reset. It is, therefore, seen thatthe timer 125 will start operating when a fault oc curs but will bedeenergized if the fault is removed before the timer continues for thetime interval for which it is set. In a relay system as disclosed, thetimer 125 may be set for a 30 second interval and if the fault continuesfor thirty seconds the timer will operate to close the switch contacts130.

The contacts 130 when closed are effective to connect'relay'140 to thealternating current source. Relay 140 is the main energizing relay forthe standby unit 11. The relay 140 includes movable contact 141 whichcloses when the relay is operated and contact 142 which opens when therelay is operated. The contact 141 connects the filament supply of thestandby unit 11 to the primary power source and also connects the timer143 to the same source. The timer 143 then runs for a predetermined timeafter which it operates to close the contacts 144 thereof. The timer 143like timer 125 is shown schematic as including a projection 145 whichoperates the contact.

Contacts 144 of the timer 143 connect relay 150 to a' directcurrent-voltage source, with the relay being held closed throughoperation of contact 151 thereof which connects the relay in series withresistance 152 to the direct current voltage source. The relay 150 alsoincludes contacts 153 and 154, with the contact 153 moving away fromcontact 155 to deenergize the timer 143 and en gaging contact 156 toenergize the plate supply of the standby unit 11. The contact 154 of therelay 150 is bridged across the movable contact 142 of the relay 140.These contacts control energization of the relay 128 for energizing themain unit 10. Therefore, after the relay 140 is energized in response toaction of the timer 125 8. and the relay 150 isenergized in response tothe action of the timer 143 the energizing circuit to the winding of therelay 128 will be broken and this relay will drop out. This will causethe contact 127 to open so that the main unit 10 is deenergized.

The relay 128 includes a contact 160 which is bridged across thecontacts 130 of the timer 125. This contact closes when the relay 128drops out, and serves to hold the relay 140 operated if the fault isremoved and the timer 125 is thereby released after the main unit hasbeen deenergized. It will be noted in this connection that if the faultis removed before the timer 143 has completed the time interval, therelay 140 will be deenergized and the changeover. cycle will be stopped.This is because contacts 130 will be opened when the fault is removedand the contact 160 will not have yet closed.

Under these conditions the main unit will remain operative and theequipment will be in condition for sensing another failure. However,after the relay 128 has been released, the contact 160 thereof willcomplete the circuit through the relay 140 so that removal of the faultwill have no effect on the operation and the standby unit 11 will remainin operation until the equipment is restored to normal by an operator.

In addition to energizing the standby unit and deenergizing the mainunit, the switchover equipment is used to disconnect the main unit fromthe antenna and to connect the standby unit thereto. This isaccomplished through the contact 161 on the relay 128 which connects thewaveguide switch to the power supply when the relay 129 drops out. Thecontact 161 may also be used to disconnect terminal equipment from themain unit 10 and to connect the same to the standby unit 11. This may beaccomplished by relay 162 which, in the normal position connects theterminal equipment 15 to the main unit 10, and when the relay 162 isenergized connects the terminal equipment to the standby unit 11. As hasbeen pointed out, the relay 162 may not be necessary as it may besatisfactory to connect the terminal equipment to both the main unit andthe standby unit without interfering with the operation of either unit.The terminal equipment may in such case be continuously connected toboth units and no switching Will be required for the changeoveroperation.

Considering now the switchover equipment required at a relay station, inthe event that the standby units 31 and 35 are individually controlledin response to failure of the main units 30 and 34 respectively, it willmerely be necessary to duplicate the system shown in Fig. 6 for the eastand the west systems. Since a single amplifierrelay unit checks theintermediate frequency amplifier, the detector and the video amplifier,this unit may be connected to either input terminal 121 or 122 of theswitchover panel and the other terminal will not be used. The detectingmeans attached to power indicator 63 and mixer 42 will be connected tothe terminals and 111 as in the terminal equipment. If it is desired toprovide a single switchover panel for connecting the standby units ofboth the east and west system in the event of failure of components ofeither main unit, it will be necessary to add two more selective relayssimilar to the relays 112 and 113. These relays can be connected inparallel to the relays 112 and 113. The four selective relays willtherefore respond to the detecting means in the two power indicators 63and 66 and in the two mixers 42 of the units 30 and 34. The amplifierrelay units 76 and 81 can be connected to the terminals 121 and 122. Insuch a system failure of any component of either main unit will causethe timer to start operation and the switchover cycle will take place.The main units 30 and 34 can both be energized by the same main relayand the standby units 31 and 35 can both be energized by a singlestandby relay. The switchover panel will be connected to both waveguideswitches 32 and 36 so that in response to failure of any component ofeither main unit,- the standby units will be energized, will beconnected to the antennas, and the main units will be deenergized.

It is seen from the above that there is provided a system for detectingfailure of any component of the main unit at either a relay or aterminal station, and for automatically switching in the standby unitwhen such failure occurs. The system is particularly adapted for use atstations where an operator is not present so that communication maycontinue even though a failure occurs in the regular operatingequipment. The system is at.-

ranged so that sensing indications for various components are broughttogether and combined, and the indication of failure from any one of thesensing units causes the switchover operation to be initiated. Beforethe switchover operation is completed, the equipment continues to checkto determine Whether the fault is merely a short interruption whichissoon ,removedor isa serious failure of one ormore components. Theequipment also'makes provision for warm-up of components before standbyequipment is switched in to insure proper operation thereof. In theevent that the main equipment operates satisfactorily before the warm-upperiod is over, the switchover cycle may be stopped and the main unitwill then continue in the system. H i

Although certain embodiments of the invention have been described whichare illustrative thereof, it is obvious that various changes andmodifications can be made therein without departing from the intendedscope of the invention as defined in the appended claims.

We claim:

1. Failure sensing apparatus for a relay system which includes a portionfor receiving signals having a local oscillator, a mixer, anintermediate frequency amplifier and a detector connected in asuperheterodyne circuit, and a portion for transmitting signals having avideo amplifier and a transmitter connected in tandem in the ordernamed, with the output of the detector being connected to the input ofthe video amplifier, and in which noise is produced in the output of thedetector in the absence of a signal, said apparatus including incombination, first frequency selective means coupled to the output ofsaid mixer and operative when the amplitude of the output thereof fallsbelow a predetermined value-to indicate defective operation of saidmixer and said local oscillator, second frequency selective meanscoupled to the output of said transmitter and operative when theamplitude of the output thereof falls below a predetermined value toindicate defective operation thereof, and means for indicating defectiveoperation of said intermediate frequency amplifier, said detector andsaid video amplifier including a source of test signals coupled to saidlocal oscillator for modulating the same and third frequency selectivemeans coupled-to the output of said video amplifier and operative whenthe amplitude of said test signals and said noise signals falls below apredetermined value to indicate failure of at least one of saidintermediate frequency amplifier, said detector and said videoamplifier.

2. Failure sensing apparatus for a communication system which includes aportion for receiving signals having a local oscillator, a mixer, anintermediate frequency amplifier and a detector connected in asuperheterodyne circuit, and a portion for transmitting signals having avideo amplifier and a transmitter connected in tandem *in the ordernamed, and in which noise is produced :in

the output of the detector in the absence of a signal, said apparatuscomprising in combination, first frequency selective means coupled tothe output of said mixer and operative when the amplitude of the outputthereof falls below a predetermined value to indicate defectiveoperation of said mixer and said local oscillator, second frequencyselective means coupled to the output of said transmitter and operativewhen the amplitude of the output thereof falls below a predeterminedvalue to indicate defective operation thereof, means for indicatingdefective operation of said intermediate frequency amplifier and saiddetector including means for applying a test signal to said localoscillator for modulatlng the same and third frequency selective meanscoupled to the output of said detector and operative when the amplitudeof said test'signal and said noise signals falls'below a predeterminedvalue to indicate failure of at least one of .said intermediatefrequency amplifier and said detector,

and means for indicating defective operation of said video amplifierincluding means for applying a test signal to the input of said videoamplifier and fourth frequency selective means coupled to the outputofs'aid video amplifier and operative when theamplitude of-saidtestsignal falls below a predetermined value to indicate failure of saidvideo amplifier.

'3. A radio relay station comprising in combination ant tenna means, amain unit, a standby unit, switching means normally connectingsaid mainunit to saidantenna means and operable to connect said standby unit tosaid antenna means, each of said units including a receiving portion, a

said receiving portion to the input of said transmitting portion, saidreceiving portion having a local oscillator, a mixer, an intermediatefrequency amplifier and a detector connected in a superheterodynecircuit and being effective to produce noise at the output of saiddetector in the absence of a signal of the desired frequency, saidtransmitting portion having a video amplifier'and a transmitteroscillator connected in tandem in the order named, and means'foroperating said switching means to connect said standby unit to saidantenna means in response to failure of "components 'of said main unitincluding, a source of test signals coupled to said local oscillator ofsaid main unit, and frequency selective means coupled to the output ofsaid video amplifier of said main unit and to said switching means foroperating said switching means to connect said standby unit when saidtest signals and'said noise signals are not present in the output ofsaid video amplifierl 4. A radio relay station comprising in combinationantenna means, almain unit, a standby unit, switchingmeans normallyconnecting said main unit to said antenna means and operable to connectsaid standby unit to said antenna means, each of said units including areceiving portion, a transmitting portion and means coupling the outputof said receiving portion to the input of said transmitting portion,said receiving portion being of the superheterodyne type and having alocal oscillator and a detector, and being effective to produce noise atthe output of said detector'when a signal is not received, saidtransmitter portion having a video amplifier, and means for operatingsaid switching means to connect said standby unit to said antenna meansin response to failure of components of said main unit including, asource of low frequency signals coupled to said local oscillator of saidmain unit, and a sensing unit coupled to the output of said videoamplifier of said main unit, said sensing unit including frequencyselective amplifier means for producing a predetermined output inresponse to said low frequency sigrials and said noise signals,rectifier means, and relay means connected through said rectifier meansto said frequency selective amplifier means and rendered operative inresponse to said predetermined voltage, said relay means being coupledto said switching means for operating said switching means to connectsaid standby unit when the output of said video amplifier falls belowsaid predetermined value.

'5. A radio relay station comprising in combination antenna means, amain unit, a standby unit, switching means normally connecting said mainunit to said antenna means and operable to connect -saicl standby unitto said antenna means, ,each of said units including a receivingportion, a transmitting portion and means coupl ng the output of saidreceiving portion to the input of said transmitting portion, saidreceiving portion operating at a predetermined frequency and having alocal oscillator, a

mixer, an intermediate frequency amplifier and a detector connected in asuperheterodyne circuit and being effective to produce noise at theoutput of said detector in the absence of a signal of the predeterminedfrequency,

said transmitting portion having a video amplifier and a transmitteroscillator connected in tandem 1n the order named, and sensing means foroperating saldswitching ,means to connect said standby unit to saidantenna means in response to failure of components of said main unit,said sensing means including portions connected individually to saidmixer and said transmitter oscillator of said. main unit and responsiveto the outputs thereof, and a further portion including a source of testsignals coupled to said local oscillator of said main unit and frequencyselective means coupled to the ouput of said video amplifier of saidmain unit and responsive to said test signals and noise in the output ofsaid video amplifier, said sensing means being coupled to said switchingmeans for operating said switching means to connect said standby unit inresponse to failure of any component of said main unit.

;6.-Radio relay apparatus comprising in combination antenna means, amain unit, a standby unit, switching means normally connecting said mainunit to said antenna means and operable to connect said standby unit tosaid antenna means, each of said units including a receiving portion, atransmittingportion and means interconnecting said portions, saidreceiving portion operating at a predetermined frequency and having alocal oscillator, a mixer, an lntermediate frequency amplifier and adetector con- ;transmitting portion and means coupling ,the output of 86nected in a superheterodyne circuit, and being effective '11 to producenoise at the output of said detector in the absence of a signal of thepredetermined frequency, said transmitting portion including a videoamplifier and a transmitter oscillator connected in tandem in the ordernamed, and means for operating said switching means to connect saidstandby unit to said antenna means in response to failure of componentsof said main unit including a source of test signals coupled to saidlocal oscillator of said main unit for modulating the same, and asensing unit coupled to the output of said video amplifier of said mainunit, said sensing unit including frequency selective means responsiveto said test signals and said noise signals, and relay means connectedto said switching means for operating said switching means to connectsaid standby unit when said test signals and said noise signals are notpresent in the output of said video amplifier, said switching meansincluding timer means for delaying operation thereof until said failurehas continued for a predetermined time interval.

7. Communication apparatus comprising in combination antenna means, amain unit, a standby unit, terminal equipment, switching means normallyconnecting said main unit to said terminal equipment and to said antennameans and operable to connect said standby unit to said terminalequipment and to said antenna means, each of said units including areceiving portion, and a transmitting portion, said receiving portionoperating at a predetermined frequency and having a local oscillator, amixer, an intermediate frequency amplifier and a detector connected in asuperheterodyne circuit, and being effective to produce noise at theoutput of said detector in the absence of a signal of the predeterminedfrequency, said transmitting portion including a video amplifier and atransmitter oscillator connected in tandem in the order named, and meansfor operating said switching means to connect said standby unit to saidterminal equipment and said antenna means in response to failure ofcomponents of said main unit including, a source of test signals coupledto said local oscillator of said main unit for modulating the same, anda sensing unit coupled to the output of said video amplifier of saidmain unit, said sensing unit including frequency selective meansresponsive to said test signals and said noise signals, and relay meansconnected to said frequency selective means and ,to said switching meansfor operating said switching means to connect said standby unit whensaid test signals and said noise signals are not present in the outputof said video amplifier, said switching means including timer means fordelaying operation thereof until said failure has continued for apredetermined time interval. Y

8. Communication apparatus comprising in combination antenna means, amain unit, a standby unit which requires energization for apredetermined time before .it is operative, a source of potential,switching means normally connecting said main unit to said source ofpotential and to said antenna means and operable to connect said standbyunit to said source of potential and to said antenna means, each of saidunits including a receiver portion, a transmitting portion and meansinterconnecting said portions, said receiving portion operating at apredetermined frequency and having a local oscillator, a mixer, anintermediate frequency amplifier and a detector connected in asuperheterodyne circuit and being effective 'to produce noise at theoutput of said detector in the absence of a signal of the predeterminedfrequency, said transmitting portion including a video amplifier and atransmitter oscillator connected in tandem in the order named, and meansfor operating said switching means to connect said standby unit to saidsource of potential and said antenna means in response to failure ofcomponents of said main unit including a source of test signals coupledto said local oscillator of said main unit, and frequency selectivemeans responsive to said test signals and to said noise signals coupledto the output of said video amplifier and to said switching means forinitiating operation of said switching means when said test signals andsaid noise signals fall below a certain amplitude thereby indicatingdefective operation, said switching means including timer meansinitiated by said frequency selective means, interruptor meanscooperating with said timer means for intermittently releasing saidswitching means during a particular time interval, contact means forconnecting said standby unit to said source of potential after saiddefective operation continues for said particular time interval, andmeans" '12 for connecting said standby unit to said antenna means andfor disconnecting said main unit from said source of potential aftersaid standby unit has been energized for said predetermined time.

9. Radio communication apparatus comprising in combination antennameans, a main unit, a standby unit including a portion which requiresenergization for a predetermined time before it is operative, a sourceof potential, switching means normally connecting said main unit to saidsource of potential and to said antenna means and operable to connectsaid standby unit to said source of potential and to said antenna means,each of said units including a receiving portion and a transmittingportion, said receiving portion operating at a predetermined frequencyand having a local oscillator, a mixer, an intermediate frequencyamplifier and a detector connected in a superheterodyne circuit andbeing effective to produce noise at the output of said detector in theabsence of a signal of the predetermined frequency, said transmittingportion including a video amplifier and a transmitter oscillatorconnected in tandem in the order named, and sensing means for operatingsaid switching means to connect said standby unit in response to failureof components of said main unit, said sensing means including portionsconnected individually to said mixer and said transmitter oscillator ofsaid main unit and responsive to the outputs thereof for checkingoperation of said local oscillator, said mixer and said transmitteroscillator, and a further portion for checking operation of saidintermediate frequency amplifier, said detector and said videoamplifier, said further portion including a source of test signalscoupled to said local oscillator of said main unit and frequencyselective means coupled to the output of said video amplifier of saidmain unit and responsive to said test signal and noise signals in theoutput of said video amplifier, said switching means including timermeans initiated by said sensing means, interruptor means cooperatingwith said timer means for intermittently releasing said switching meansduring a particular time interval, contact means for connecting saidportion of said standby unit to said source of potential after saiddefective operation continues for said particular time interval, andmeans for connecting said standby unit to said antenna means after saidportion of said standby unit has been energized for said predeterminedtime.

10. Communication apparatus comprising in combination antenna means, amain unit, a standby unit having a portion which requires energizationfor a predetermined time before it is operative, a source of potential,switching means normally connecting said main unit to said source ofpotential and to said antenna means and operable to connect said standbyunit to said source of potential and to said antenna means, each of saidunits including a receiving portion and a transmitting portion, saidreceiving portion operating at a predetermined frequency and having alocal oscillator, a mixer, an intermediate frequency amplifier and adetector connected in a receiver circuit and being effective to producenoise at the output of said detector in the absence of a signal of thepredetermined frequency, said transmitting portion including a videoamplifier and a transmitter oscillator connected in tandem in the ordernamed, and sensing means including portions coupled to said receivingportion and said transmitting portion of said main unit and responsiveto failure of said components of said receiving portions and saidtransmitting portion, said sensing means being connected to saidswitching means to connect said standby unit to said antenna means inresponse to failure of components of said main unit, said switchingmeans including timer means initiated by said sensing means, interruptormeans cooperating with said timer means for intermittently releasingsaid switching means during a particular time interval, contact meansfor connecting said portion of said standby unit to said source ofpotential after said defective operation continues for said particulartime interval, and means for connecting said standby unit to saidantenna means after said portion of said standby unit has been energizedfor said predetermined time.

11. Radio relay apparatus comprising in combination antenna means, amain unit, a standby unit, a source of potential, switching meansnormally connecting said main unit to said source of potential and tosaid antenna means and operable to connect said standby unit to saidsource of potential-and to said antenna means, each of said units 13including a receiving portion, a transmitting portion and meansinterconnecting said portions, said receiving portion operating at apredetermined frequency and having a local oscillator, a mixer, anintermediate frequency amplifier and a detector connected in asuperheterodyne circuit and being effective to produce noise at theoutput of said detector in the absence of a signal of the'predeterminedfrequency, said transmitting portion including a video amplifier and atransmitter oscillator connected in tandem in the order named, and meansfor operating said switching means to connect said standby unit to saidsource of potential and said antenna means in response to failure ofcomponents of said main unit including a source of test signals coupledto said local oscillator of said main unit, and frequency selectivemeans responsive to said test signals and to said noise signals coupledto the output of said video amplifier and to said switching means forinitiating operation of said switching means when said test signals andsaid noise signals fall below a certain amplitude thereby indicatingdefective operation, said switching means including timer meansinitiated by said frequency selective means, interrupting meanscooperating with said timer means for intermittently releasing saidswitching means during a particular time interval, and means forconnecting said standby unit to said source of potential and to saidantenna means after said defective operation continues for saidparticular time interval.

12. A radio relay system comprising in combination antenna means, a mainunit, a standby unit, switching means normally connecting said main unitto said antenna means and operable to connect said standby unit to saidantenna means, each of said units including a receiving portion having alocal oscillator, a mixer, an intermediate frequency amplifier and adetector connected in a superheterodyne circuit, and being effective toproduce noise signals at the output of said detector in the absence of adesired signal, and means for operating said switching means to connectsaid standby unit to said antenna means in response to failure ofcomponents of said main unit including a source of test signals coupledto said local oscillator of said main unit for modulating the same and asensing unit coupled to the output of said detector of said main unit,said sensing unit including frequency selective means responsive to saidtest signals and said noise signals, and relay means connected to saidfrequency selective means and to said switching means for operating saidswitching means to connect said standby unit when said test signals andsaid noise signals are not present in the output of said detector, saidswitching means includ ing timer means for delaying operation thereofuntil said failure has continued for a predetermined time interval.

13. A radio relay system comprising in combination, antenna means, amain unit, a standby unit having a portion which requires energizationfor a predetermined time before it is operative, a source of potential,switching means normally connecting said main unit to said source ofpotential and to said antenna means and operable to connect said standbyunit to said source of potential and to said antenna means, each of saidunits including a receiving portion, a transmitting portion, and meansinterconnecting said portions, said receiving portion having a localoscillator, a mixer, an intermediate frequency amplifier and a detectorconnected in a superheterodyne circuit, said receiving portion producingnoise signals at the output of said detector in the absence of a desiredsignal, said transmitting portion including a video amplifier and amodulator connected in tandem in the order named, and means foroperating said switching means to connect said standby unit to saidsource of potential in response to failure of components of said mainunit including a source of test signals coupled to said local oscillator of said main unit and a sensing unit coupled to the output ofsaid video amplifier of said main unit, said sensing unit includingfrequency selective means responsive to said test signals and said noisesignals and relay means connected to said frequency selective means andto said switching means for initiating operation of said switching meanswhen said test signals and said noise signals in the output of saidvideo amplifier fall below a predetermined level, said switching meansincluding first and second timer means, said first timer means causing.operation of said switching means to connect said portion of saidstandby unit to said source of potential and to 1114 initiate operationof said second timer means after said failure has continued for aparticular time interval, said second timer means causing operation ofsaid switching means to connect said standby unit to said antenna meansand deenergize said main unit after said failure has continued for saidpredetermined time after said second timer started operation.

erating-said switching means to connect said standby unit to said sourceof potential in response to failure of components of said main unitincluding a source of test signals connected to the input of said signalchannel in said main unit and a sensing unit coupled to the output ofsaid signal channel of said main unit, said source of test signalsoperating continuously during operation of said main unit tocontinuously test the same, said sensing unit including frequencyselective means responsive to said test signals and relay meansconnected to said frequency selective means and to said switching meansfor initiating operation of said switching means when said test signalis not present in the output of said signal channel of said main unit,said switching means including first and second timer means, said firsttimer means causing operation of said switching means to connect saidstandby unit to said source of potential and to initiate operation ofsaid second timer means after said failure has continued for aparticular time interval, said second timer means causing operation ofsaid switching means to connect said standby unit to said antenna meansand deenergize said main unit after said failure has continued for saidpredetermined tlme after said second timer started operation.

15. A microwave relay station adapted to operate continuously without anoperator in attendance including in combination, antenna means, a mainreceiver-transmitter unit, a standby receiver-transmitter unit,switching means normally connecting said main unit to said antenna meansand operable to connect said standby unit to said antenna means, saidmain receiver-transmitter unit including a receiving portion foroperation at a first frequency and having a local oscillator, a mixer,an intermediate frequency amplifier, and a detector connected to asuperheterodyne circuit, a transmitting portion for operation at asecond frequency and having a video amplifier and a transmitteroscillator connected in tandem in the order named, means connecting theoutput of said detector to the input of said video amplifier, saidreceiving portion provlding noise at the output of said detector at asubstantially fixed level in the absence of a signal of said firstfrequency, a source of test signals coupled to said local oscillator formodulating the same, said receiving portion providing said test signalsat the output of said detector at a given level in the presence of asignal of said first frequency and at a much lower level in the absenceof a signal of said first frequency, whereby said test signals and noiseare alternately present in said detector output in accordance with thepresence and absence of a received signal of said first frequency, saidnoise and test signals being applied from said detector to said videoamplifier and amplified therein, and a sensing unit coupled to theoutput of said video amplifier including a selective amplifier andvoltage responsive means, said selective amplifier having an inputcircuit coupled to said video amplifier and producing a voltage inresponse to said test signals and noise, said voltage reaching asubstantially constant predetermined value substantially independent ofthe level of received signals when the components of the equipmentincluding said intermediate frequency amplifier, said detector, and saidvideo amplifier operate effec tively, and said voltage falling to asmaller value when any one of said components operates defectively, saidvoltage responsive means being coupled to said selective amplifier andoperatively connected to said switching means for holding said switchingmeans in a normal position connecting said main unit to said antennameans when said predetermined voltage is produced and for causingoperation of said switching means to connect said standby unit to saidantenna means when said smaller voltage is produced.

16. Radio receiving equipment adapted to operate continuously without anoperator in attendance including in combination, antenna means, a mainreceiver unit, a standby receiver unit, switching means normallyconnecting said main unit to said antenna means and operable to connectsaid standby unit to said antenna means, said main receiver unitincluding a local oscillator, a mixer,

an intermediate frequency amplifier, and a detector connected in asuperheterodyne circuit, said receiver unit providing noise at theoutput of said detector at a substantially fixed level in the absence ofa signal of said first frequency and at a much lower level in thepresence of a signal of said first frequency, a source of test signalscoupled to said local oscillator for modulating the same, said receivingportion providing said test signals at the output of said detector at agiven level in the presence of a signal of said first frequency and at amuch lower level in the absence of a signal of said first frequency,whereby said test signals and noise are alternately present in saiddetector output in accordance with the presence and absence of areceived signal of said first frequency, and a sensing unit coupled tothe output of said detector including a selective amplifier and voltageresponsive means, said selective amplifier having an input circuitcoupled to said detector and producing a voltage in response to saidtest signals and noise, said voltage reaching a substantially constantpredetermined value substantially independent of the level of receivedsignals when the components of the equipment including said intermediatefrequency amplifier, and said detector operate effectively, and saidvoltage falling to a smaller value when any one of said componentsoperates defectively, said voltage responsive means being coupled tosaid selective amplifier and operatively connected to said switchingmeans for holding said switching means in a normal position connectingsaid main receiver unit to said antenna means when said predeterminedvoltage is produced, and for causing operation of said switching meansto connect said standby unit to said antenna means when said smallervoltage is produced.

References Cited in the file of this patent UNITED STATES PATENTS2,131,109 Lowell Sept. 27, 1938 2,148,532 Chaft'ee Feb. 28, 19392,227,381 Rider et a1. Dec. 31, 1940 2,252,811 Lowell Aug. 19, 19412,379,069 Dysart June 26, 1945 2,508,853 Bond et al. May 23, 19502,597,043 Treadwell May 20, 1952

